Chapter 2 : Configuring a Network Operating System
Notes on Chapter 2.0 2.0.1 Home networks connect end devices. In a home network there are 4 types of non-end devices. Router '- Recieves data packets then resends them to and from the internet. '''Switch '- Connects end devices. 'Wireless Access Point '- Uses a radio transmitter to wirelessly connect with end devices. 'Firewall Appliance '- Secures outgoing traffic and restricts incomming traffic. Often these devices are contained in the same physical object in a small home environment but in larger networks for companies each device has it's own phsyical object in the network. 2.1 2.1.1 User talks to shell. Shell talk to kernal. Kernal talks to hardware. User --> Shell --> Kernal --> Hardware CLI = Comand Line Interface. Used to interact with Cisco ISO (Internetwork Operating System). GUI = Graphical User Interface. Used in home environments to interact with a router's firmware. OS preforms behind the scenes functions that are highly technical, e.g. moving a mouse. Cisco OS does it as well for routers and switches so we can just use their functionality without getting technical. There are many versions and types of IOS but we will mostly be using Cisco IOS Release 15.x. The Cisco OS is stored on a flash drive and copied into RAM at runtime. The Cisco OS has many uses, these include: *Providing Network Security. *IP addressing of virtual and physical interfaces. *Enabling interface-specifica configurations to optimize connectivity of the respective media. *Routing. *Enabling quality of service technologies (different service to different types of requests). *Supporting network management technologies. 2.1.2 Meathods to access the CLI environment: *Console *Telenet or SSH *AUX port '''Console Console is used through the ethernet port and is for direct access to the IOS. It is an 'out of band' connection and can be used when there are no current network configorations set up. It is used for initial configoration or for instances of failure. A password can be set for security but i can be bypassed so the device should be physically secured to prevent unauthorized physical access. Telenet Telenet aloows remote access through an active internet adress (e.g. IPv4). A device must have active network services to use telenet. Telenet also allows the use of a client. A network administrator can allow another device that supports telenet server processes to use the CLI. SSH (Secure Shell) SSH is a protocol similar to Telenet but much more secure. It uses stronger password authentication as well as encryption so that data cannot be viewed by unauthorized devices. If possible, always use SSH rather than Telenet. AUX AUX (Auxiliary) can access the CLI through a telephone dialiup connection. This is used for remote 'out of band' CLI access. Locally the Console is prefered because it always displays startup, debugging and error messages by default. 2.1.3 The Cisco IOS has many modes in a hierarchical structure: *User executive *Privileged executive *Global config *Specific config Commands have scope to modes including calling the next mode down. Secuity can be applied to each level of mode. User EXEC Mode Used for basic monitoring commands. No security requried to access User EXEC by default but it is good practice to set some up. Defined by the CLI prompt ending with > (e.g. Switch>). Privileged EXEC A user must go through User EXEC mode then go into Privileged EXEC. There is no authentication required to access Privileged EXEC by default but it is a good idea to set some up. Defined by the CLI prompt ending with # (e.g. Switch#). Global Config From this mode configurations are made that affect the whole device. Has to be accessed through Privileged EXEC. Defined by format : Switch(config)# Specific Config Specific config is a group of modes that all have different functions. Each one must be accessed from the Global Config mode. Defined by format : Switch(config-mode)# "enable" and "disable" are used to move betwween User and Privileged EXEC modes. "exit" moves up from any config or quits from any EXEC. "end" moves from any submode to Priv EXEC. 2.1.4 Lines in the CLI have this format: Promt --> Command --> Space --> Keyword or Argument. To navigate to the Command Reference and find a particular command follow the steps below: Step 1. Go to www.cisco.com. Step 2. Click Support. Step 3. Click Networking Software (IOS & NX-OS). Step 4. Click 15.2M&T (for example). Step 5. Click Reference Guides. Step 6. Click CommandReferences. Step 7. Click the particular technology that encompasses the command you are referencing. Step 8. Click the link on the left that alphabetically matches the command you are referencing. Step 9. Click the link for the command.